(1) Field of the Invention
This invention relates to a trench power semiconductor structure and a fabrication method thereof, and more particularly relates to a trench power semiconductor structure with high switching speed and a fabrication method thereof.
(2) Description of the Prior Art
Switching speed is an important characteristic for the application of trench power semiconductor devices. The enhancement of switching speed is helpful for improving switching loss of high frequency applications. FIG. 1 is a cross-section view of a typical n-channel trench metal-oxide-semiconductor field effect transistor (MOSFET). As shown, the n-channel trench MOSFET has an n-type drain region 110, a p-type body region 120, an n-type source region 130, a metal layer 140 coupled to a source electrode, a gate oxide layer 150, and a polysilicon gate 160.
At the moment that the MOSFET is being switched off, a reverse current is generated to remove the excessive minority carriers in the body diode. However, restricted by the body diode, it is hard to reduce the source-to-drain forward voltage (VFSD) of the trench power semiconductor structure below 0.75V. Thus, an apparent time period is usually demanded for removing the excessive minority carriers and thus the switching speed of the power MOSFET is thus restricted by the reverse recovery ability of the power MOSFET, which also results in the increasing of switching loss.
Accordingly, it is eager for the skilled in the art to find out a reliable trench power semiconductor structure with low source-to-drain forward voltage (VFSD) and acceptable breakdown voltage to overcome the above mentioned drawbacks.